Best car seat for non-drivers/occasional use

Expecting first baby in August. We don't have a car and rely on buses, but need to get a car seat to a) be allowed out of the hospital b) for granny and granddad's car.

Already have a secondhand travel system (Silvercross 3d ) so don't know whether to just buy a new seat for that, or whether we'd be better buying a 0+/1 reversible.

I'm planning to mostly use a sling, so it doesn't really matter if car seat is pram-compatible as it will just be used in parents' car (or does it?) Although have just thought we should probably have another one at ours in case of going in other people's car/taxi! Was thinking of getting this one:

We don't have a huge budget, but obviously prepared to pay however much we need for baby to be safe. Is it better to go for separate infant seat (maybe the Silvercross) and then think about a second one when baby is bigger, or invest in one now that will see us through to being a toddler.

Ooh also, probably good to have one that is light to carry in case we need to take it on bus in order to get to somewhere where we'll be using car IYSWIM I have the beginnings of some ab/pelvis/back problems so am expecting I may not be able to carry heavy things (possibly including baby so may need to give up on sling plan!)

Have a look here As you're looking at a use every now and again cheaper end of the market have a look at the joie seats. They offer rear facing up to 18kg (about 4 years) and are very competitively priced. The everystage for example will take you from birth to not needing a car seat anymore about about 12 years for £200, stages birth to around 7 years for £150 and the steadi or tilt up to about 4 years for less than £100 but all can be rear facing to 18kg. I have the steadi as a holiday/grandmas car seat because it's lightweight, compact and easy to move. But I wouldn't want use it for an every day car seat.

There's a Facebook group called car seat advice for mummies and daddies, you might find helpful to message them with all the details and see what they recommend.